YOUNGSTOWN, Ohio (WKBN) – Winter has returned to the Valley as we just experienced our fifth day in a row of snow. In fact, the 3.9 inches of snow that have been recorded at the Youngstown/Warren Regional Airport in March is nearly 10 times the amount of snow that fell during the entire month of February.

Throughout the colder months, there are many different shapes and sizes of snowflakes that fall. Monday, you may have noticed that there were periods of big snowflakes and small snowflakes.

What is the reason behind different-sized snowflakes, and when are large flakes more likely to fall?

The answer to this question has a long and storied history. We are not the first to wonder why there are different-sized snowflakes. One of the pioneers in the science of snow crystal growth was Ukichiro Nakaya, a Japanese scientist who conducted groundbreaking research on the formation and morphology of snowflakes.

Originally, Nakaya studied X-ray technology in school. Then, he took a job at Hokkaido University as an assistant professor, and everything changed.

See, the university had few pieces of equipment and even fewer research funds. What the university did have was an abundance of snow. Needing an outlet to focus his scientific mind, Nakaya immediately began research on the formation of snowflakes.

By 1954, Nakaya had compiled enough research to write a 510-page book called “Snow crystals: Natural and Artificial,” which was published by Harvard University. You can still buy the book today. He is even credited with developing the first artificial snowflake.

One of the biggest takeaways from the book is the graph below which shows the relationship between temperature, water vapor and snowflake size/shape:

Original Nakaya snowflake morphology graph from his book “Snow crystals: Natural and Artificial” published in 1954.

Now, on this graph, “supersaturation” is just another word for moisture. Also, keep in mind that the temperature on this graph represents the temperature where the snow forms and not the temperature on the ground.

The biggest takeaway from this graph is that there is a special combination of water vapor in the atmosphere and temperature that produces big snowflakes. If the temperature is too warm and there is not enough moisture, then the snowflakes are small. Additionally, if the temperature is too cold, then the snowflakes are small.

If there is ample moisture in the atmosphere and the temperature is between -10°C (14°F) and -20°C (-4°F) in the cloud then large and iconic snowflakes are produced.

Around midday Monday, the moisture in the atmosphere was reduced, and there were warmer temperatures. Therefore, small dendrites formed like the ones seen on the graph between the temperature of 0°C and -5°C.

Below is an example of small dendrite snowflakes:

Example of small dendrite snowflakes (Photo was taken by Adam Clayton on February 22, 2019).

Eventually, the atmosphere began to cool Monday afternoon, and as a storm system pushed into the Valley, more moisture was introduced. These factors led to the growth of larger dendrite snowflakes like the ones in the graph above.

Another factor that leads to large snowflakes is the combination of smaller snowflakes to produce larger ones. This process is called aggregation.

Aggregation occurs when there is ample moisture in the atmosphere across different sub-freezing temperature ranges. When this occurs, the Nakaya graph shows that snowflakes of different shapes and sizes will form. Different-sized snowflakes moved at different speeds as they fall from the cloud to the ground. This leads to snowflakes sticking together to form aggregates.

Below is an extreme example from Colorado:

Large aggregate snowflakes. The video was taken by Adam Clayton on March 29, 2019.

The next time it is snowing outside, pay attention to what the shapes of the flakes look like. This will give you a window into how they were created.